FIG. 8 illustrates a conventional method of selectively coating alternating light-emitting facets disposed on the same surface of an array of semiconductor lasers. In FIG. 8, a laser device 1 includes two lasers, one laser having a light-emitting region 2 for emitting a relatively high power output light beam. The other laser includes a relatively low power, low noise light-emitting region 3. The facets of the light-emitting regions at surface 4 through which light is emitted are selectively coated with different coatings. In FIG. 8, the light-emitting region 2 facet at surface 4 is coated with a relatively low reflectance film while no coating is deposited on the relatively low power light-emitting region 3 facet on surface 4. The individual laser device 1 is manufactured as one of a relatively large number of such devices in a semiconductor wafer or bar 6 in FIG. 8. It is desirable to coat each of the relatively high power light-emitting region facets in a single step.
As illustrated in FIG. 8, each of the light-emitting region 2 facets on surface 4 is simultaneously coated by positioning a mask 8 having a regular pattern of openings so that one of the openings is aligned with each of the high power light-emitting region facets. A source of coating material 7 is then evaporated and the evaporated material 9 passes through the openings in mask 8 to deposit the coating 5 without coating the low power light-emitting region 3 facets on surface 4.
The process illustrated in FIG. 8 requires that the openings in mask 8 be accurately aligned with light-emitting region 2 facets. This registration is difficult to achieve since the light-emitting regions are typically only a few microns in width and the separation between light-emitting regions 2 and 3 may be as small as only a few microns. Therefore, a slight misalignment in the mask relative to the light-emitting regions can result in improper coating of many or all of the simultaneously coated light-emitting region facets.